Why can't my best friend find a guy that isn't a loser?

My best friend has been talking to me and feeling so upset lately. She's so pretty and she's one of the nicest people I know, but she keeps getting really upset because it seems she attracts only losers? They're always douchebags that don't really care about her, and seeing her get her heart broken makes me feel so sad. She doesn't chase guys at all, but whenever she gets male attention it's only from these loser assholes. They're not attractive either, but she always says she doesn't even care about looks she just wishes guys that are actually nice would approach her. But they never do? I've got a boyfriend and she says she wishes she could be happy as well, what helpful advice could I give her?why do you think only idiots seem to be coming after her?